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Glossary
The following are a list of useful terms and definitions in the world of pottery.
To jump forward to a certain term in this alphabetized list, use the links below:
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Alumina—along with silica, a basic building block of clay and glaze. Alumina doesn't melt at temperatures used for ceramics and glazes, reduces flow (fluxing) in glazes, and helps with strength.
Amphora—used in Mediterranean countries, this pot was used for storing and transporting liquids. Typically two handles were linked from the neck to the body of the pot.
Arabesque—this is ornamentation that is characterized by smooth running, linear designs of scrolls or leaves. The use of flowers and foliage in this style produce intricate patterns of interlaced lines.
Ark—a tank used for the storage of clay or glaze slips. There is often a continuous stirring that occurs mechanically that prevents the slip from settling.
Barbotine decoration—using a fine nozzle, thick slip is dragged along in streams onto a leather hard pot.
Ball Clay—this is a general term used for many clays. Ball clay is actually blue. This is usually light in color and highly plastic. Unfortunately by itself, it is too slippery and fine for use, unless it is combined with sand, grog and coarser less plastic clays.
Basalt ware—stoneware that is black and unglazed. About 50% of the clay is vitrified and colored by 50% of iron and manganese oxides. The originator of this ware was Josiah Wedgwood.
Batwash—kiln shelves become sticky from glaze droppings. To prevent the sticking of ware put into the kiln it is necessary to use batwash on the shelves. This is a mixture of flint and water.
Beading—extreme crawling, which causes the glaze to roll back in on itself. Odd shaped raised globs form on a bare pot.
Biscuit—typically soft and porous, this term applies to pottery that has been fired only once without a glaze. Due to its porosity it is easier to get a glaze to adhere to it. The temperature range for firing is 850 C to 1000 C (1562 F to 1832 F).
Bisque—fired pottery that is unglazed. This term deals mostly with industrial methods of high temperature firing of the unglazed ware followed by lower temperatures for glazing. There are advantages to this type of firing, such as: the ware is easier to handle due to the hardness, warping from shrinkage can be controlled a little easier by setting the pieces in sand during the firing, and since there is a completion of shrinkage the glaze firing can be more economically set.
Bocarro—red unglazed stoneware which originated from 17th- century china. This term is now commonly used for any vitrified red clay ware.
Bole—an impalpable powdery red clay. Found in eastern Mediterranean countries. It is used in the compounding of enamel colors and also as a pigment.
Boxing—rim to rim nestling of bowls or cups to prevent warping while drying and firing.
Body—the basic material from which any ceramic piece is made. Fundamentally this is clay, usually natural materials and other ceramic materials, combined for specific properties for forming and firing.
Burning off—loose terminology for the simple removal of bound water in the ceramic change.
Burning out—this is where unwanted matter is removed by the use of heat in the kiln. An example would be, the creation of some colors using gums and oils. They would be convenient carriers of the colors when applied however they would need to be burnt out by oxidation at temps above red heat. If they were not burnt out, they would damage the glaze, body or color by bubbling, blistering and possible discoloration.
Burnishing—by rubbing leather hard clay with a hard object like a smooth pebble or back of a spoon a polished appearance would occur.
Butterfly—this is a type of glaze crawl that leaves its place and folds back on itself, leaving double thickness and a bald patch.
Cane Clay—sand-like in texture, this is a refined fireclay, (it is less refractory than fireclay). When fired, the color is that of straw or cane.
Carinate—this is a pottery shape that is made by the joining of straight inward shaped walls to a round base.
Celadons—an overall term used typically for oriental stonewares, and porcelains with green glazes. The color is acquired by the use of small amounts of iron in the glaze.
Chamotte—Grog. This is a fired fireclay. (Other types of refractory clay) Due to Scandinavian usage the term chamotte ware or chamotte also applies to artistic wares made up of coarsely grogged clay.
Chattering—this is a rippling effect that appears when turning. If the clay is either too hard or soft this will occur, especially if a blunt, or hard tool is used on clay that is too soft, or one that is too flexible is used on hard clay. Chattering can be used deliberately however as decoration.
Cheese hard—this stage of clay can be carefully handled without deformation, due to it being dried sufficiently from its plastic state. It is the softest stage at which it can be shaved, or turned on a lathe, or wheel. Optimum drying would be leather hard stage.
China—this actual term originates from the habit of naming imports by their countries. To potters the implication of this word is that of a translucent white body covered with a glaze fired lower in temperature than the body.
China Clay—this is the purest of all natural clay.
Cinerary urn—this is a pot that was used primarily for the burial of cremated remains. This urn has been found all over the world. They have been found in all sizes, some as small as 5 cm tall, to vessels as tall as 50 cm. The best example of this type of urn comes from the Middle Bronze age of South Wales, Britain, 1400-1000 B.C.
Cistercian ware—deep red clay that is thinly potted, it has a glaze that is dark and shiny, which contains iron and manganese oxides. This is earthenware that was made in some cases by Cistercian monks during the 16th century.
Clair-de-lune flush—this is a romantic term used in the 19th century to describe pale blue stripes (distinguishable from the surrounding colors--striations). This can be found in Chinese stoneware glazes.
Clay—a natural material of earth, that becomes plastic when moistened and hard when fired, such as: brick, tile and pottery. Composition is hydrous aluminum, silicates and other minerals.
Clobbering—the intention of this term is not meant to be complimentary. This was something that was done mostly in the 18th and 19th centuries. People would add decoration to someone else^s already finished pottery, in the hopes of giving the item an added boost to increase the value of the piece.
Coiling—a hand building technique used to make pots. Plastic "snakes" of clay are used. They can vary from a thin strip to a large sausage like strip. It is hand manipulated, pinched and squashed together to form a pot without the coil like look from how it was started, though in some cases the clay can be left snakelike for the decorative look. Typically this is started at the base of the pot and built upwards.
Cornish Stone—the usage of this feldspathoid is that of a flux in bodies but is also a major element in glazes. Contents include quartz, feldspar, mica, kaolinite with a small percentage of fluorspar. Upon melting (at 1150 C to 1300 C ~~2102 F to 2372 F) this becomes a stiff glass which is opaque in appearance with suspended fine bubbles
Costrel bottle—this is a bottle that has lugs (handles) near the or neck. Often used by people traveling in days of old. The origin is post-classical Greece. They came in many shapes and sizes.
Crackle—this is just what it sounds like, if you were to take a piece of paper and crackle it up, crunch it up, upon straightening that paper out, you would end up with a similar look to a pot where the glaze has been crazed. With lines going every which way. Raku ware often has this feature.
Crawling—the surface effect when a glaze pulls apart from a continuous surface into many nearby sections with voids in between—a bit like spots on a leopard. This is often, but now always, done intentionally to give the surface increased texture and interest.
Crazing—an effect similar to crawling, where the glaze cracks along many lines and into many pieces. Unlike crawling, these sections remain very close to each other and the lines in between them remain very thin, even hairline.. The effect is caused by the glaze shrinking during cooling to a greater extent than the clay underneath shrinks. The outside glaze is too small for the clay which it covers. Because the glaze covering over shrinks, it cracks. This is also described as the glaze "not fitting" the clay. This is often used intentionally to create an interesting surface texture.
Creamwear—this is the forerunner of English white earthenware today. It was developed in the 18th century, by the Astburys, and later Whieldon and Wedgwood perfected it. The recipe is made up of 25% china clay, 25% ball clay, 35% flint and 15% Cornish stone.
Deflocculant—with the addition of very little water, this substance will act chemically on plastic clay giving it liquid characteristics. Sodium silicate and sodium carbonate will have this effect.
Delftware—made in Delft, Holland, this English term is used to describe tin-glazed earthenware. Often this term is used to describe all tin-glazed ware made in England.
Dunting—the breaking or cracking of clay, from quick cooling, faults in the structure of the clay piece, effects of a glaze, etc, causing a stress on the clay great enough to break it.
Earthenware—this is one of the two main kinds of pottery. (The other being Stoneware ) Earthenware is porous, and not very dense or heavy. Its glazes are usually shiny and bright.
Elutriation—this is the division of course clay and fine clay, by putting the clay in water. The fine clay will remain suspended in the water where as the larger particles such as stones and sand will sink. A mechanical device is used in this process to move the slurry upwards against gravity.
Encaustic—decoration where the use of different colored clays are inlaid into the body clay. These inlaid pieces are actually put into cut out portions of the body, though sometimes they are just rolled onto the body. Cistercian monks used this technique while producing paving tiles.
Engobe—a surface coating usually used for decoration, but not usually considered a glaze. It is made from clay and may contain glaze or glaze components. Depending upon how the piece is fired, even though it is not a glaze, it may become glaze like or glasslike, even more so than the clay body it covers. See examples here.
Eosine—this rainbow-hued finish is named after the Greek goddess Eos (same as the Roman Aurora), the goddess of dawn. (Not the same as Eosin, the organic dye.) Eosine is the finish found on Zsolnay ceramics from world-famous Zsolnay Factory in Pêcs, Hungary.
Faience—this term describes colorfully decorated earthenware or glazes. The origin of this term is from Faenza in northern Italy. Today the style that is considered faience is the covering of surfaces with matt and shiny glazes that are often blended together.
Fat clay—highly plastic clay, long clay, that is often added to other clays to improve workability.
Feldspar—a naturally occurring mineral (aluminosicilate) formed by the decomposition of granite or igneous rocks. Composed of alumina and silicon oxides plus soda (sodium carbonate), potassium or calcium. Feldspars melt around 2150 degrees Fahrenheit (1177 Celsius) and tend not to run due to their high alumina content.
Feldspathoids—though feldspathoids have similar properties to feldspar, they are not true feldspars at all. They can be useful in glazes, but cannot be considered as true minerals due to the fact that they do not conform to unified chemical formulae.
Fettling—the removal or trimming away of excess clay.
Fireclay—simply put, this is a clay that can withstand high temperatures. These are typically refractory clays and often used for firebricks. Pale buff or "almost" white is the color that appears when fired.
Firing—the transformation of clay into a pot. The involvement of heat at least 600 C (1112 F) is required to make this alteration.
First red—when the temperature in a kiln reaches 600 C (1112 F) the pot that has been fired gives off an incandescent glow. This tells you that the point of dunting has been passed and the ceramic change is almost complete.
Flint—pure silica which contains less than 5% impurity. Its native color is black which turns to white when heated. It is usually bought in the form of powder, which is added to bodies and glazes. When added to bodies it gives a whiteness and hardness and also adds a resistance to crazing.
Flux—"flux" means flow, and thus fluxes are materials that help glazes flow. They do this by lowering the temperatures at which other minerals would naturally melt.
Fosted—if there is a hole, or slight air intake during the firing of a pot, one side may end up underfired, which will make part of the pot look lighter in appearance than the rest of the pot.
Frit—by heating two or more raw materials together, this is a manufactured glaze or body that is melted together to form a glass that is then shattered, usually by pouring into cold water. The shattered pieces are then ground into powder.
Galena—this is lead ore, impure, used to make lead glazes. In the 10th to the 17th centuries Galena was dusted on newly thrown wet ware. This fused the upper layer of clay during the firing into a glaze.
Glaze—a layer of ceramic or glass that is fused onto the surface of the clay of a pot or ceramic piece. Used to seal the piece, decorate it, or both.
Gloss—a glaze which has a smooth, shiny surface.
Grog—this is ground, already fired body that is added to clays. It can provide texture to a piece. It has many advantages in its usage. One being that since it has already been fired; it helps to cut down on the overall shrinkage.
High fire—pieces which are produced about 2305 degrees Fahrenheit (1263 Celsius) or cone 8. Typical stoneware and porcelain.
Hispano-Moresque ware—during the Moorish occupation of Spain, this lustred pottery was made (between the 8th and 15th centuries). Oddly enough both Moors and Spaniards, Christian and the Islamic part were responsible for this pottery. Over time the lustre became coppery in color.
Humper—this is a distorted plate, where the flat part has risen up in an unacceptable fashion. Usually found on pressed plates, and or plates that are glazed only on the and sides.
Inglaze—the application of ceramic colors put (usually painted) onto an unfired glaze. The colors will sink into the glaze, and stain it. These colors are pure oxides, strongly colored glazes, or stains that have been prepared for this.
Inlay—a type of decoration where the surface of cheesehard clay is scored, and filled with a thick colored slip. After the slip dries, the excess is scraped off to show the clean lines.
Jun—this is an opalescent stoneware glaze (pale blue in color). The origin of this term is from a town in northern China. This was first made in the 11th century. The glaze needs to be applied in a thick manner, otherwise the body will show through, and it will seem almost transparent.
Jutland ware—The origin of this pottery is that of Neolithic times. (Nearing the end of the Stone Age) It was perfected early on and continued to be made until the mid-20th century. This was unglazed, peat-fired pottery.
Kaki—Japanese name for persimmon fruit, also the name for the rust color that appears on the surface of stoneware glazes. This occurs when iron oxide crystals spread.
Keuper marl—this is a high quality mudstone, found during the Triassic Period (a time characterized by the appearance of dinosaurs, time of high volcanic activity). It began as a desert dust. Though not consolidated it can be reconstituted as clay. High in clay content, iron, and lime. Brown and gray when raw but brown-burning.
Kidney—a kidney-shaped tool, which can be used for finishing thrown pots as well as smoothing and pressing clay in a mold. For use in finishing thrown pots, it is made of flexible steel. When used for smoothing and pressing clay, it is made of stiff rubber.
Kiln—simply put this is a structure that is built to maintain heat. A place that has come a long way over the years, where clay is fired and turned into pots.
Kneading—clay preparation, where a lump of clay is rolled in upon itself, while stretching and pulling to get out the air bubbles.
Kochi—this is Japanese Raku ware. A hard-fired biscuit is used.
Kwaart—to give a higher gloss and depth to color, this technique was used by the Delft potters to imitate Chinese blue-and-white porcelain. To get this effect they used a clear transparent glaze over a white opaque glaze.
Leather-Hard—this is a stage midway between wet and dry clay. The clay will be stiff enough to support its own weight, but pliable enough to be bent and worked with.
Low fire—pieces which are produced above 1300 degrees Fahrenheit (704 Celsius ), but more typically from 1641 F (894 C ) and up to 1940 Fahrenheit (1060 Celsius), or cone 010 to cone 04.
Maiolica—this is a general term used for Earthenware that has been glazed with an opaque tin glaze and painted over with oxides.
Matt—a glaze which has a surface that is not shiny, although it may have some sheen, ranging from dull (very flat) to stony (with a slight sheen or patina).
Medium fire—pieces which are produced above 2014 degrees Fahrenheit (1101 Celsius) or cone 03, up to 2232 F / 1222 C, or cone 6. Typical of stoneware (which may also be fired).
Monochrome pottery—this is pottery that is typically made in one color. Where decoration is used the color is one single contrasting color.
Obsidian—a dark or black glass produced by a volcano. Consists of silica (SiO2) heated until it flows, and then cooled. See also pumice.
Opacifier—this is a substance that is typically made of a metal oxide, commonly tin oxide. When added to a clear glaze will turn the glaze opaque.
Opaque—a glaze which will not pass light, therefore blocking any color underneath it, whether of the clay, a decoration or another glaze. Glazes are typically made opaque by the addition of tin oxide or various zirconium compounds.
Oxidation—kilns are usually fired either with sufficient air for combustible materials, clay, or glaze to oxidize (burn), or not lose the oxygen atoms already bound into their molecules. Typical of electrically heated kilns, as well as gas, oil or wood fired kilns with sufficient air intake. See also reduction.
Paper Clay—by the addition of paper pulp to plastic clay (proportions of 50% to the total) there is greater plasticity, a reduction of shrinkage and an almost glue like bonding that occurs. This is especially important to hand builders and sculptors when joining pieces together.
Plasticity—this is a state of being plastic, which gives clay the ability to be molded, shaped and altered.
Porous—anything which absorbs or leaks water. In ceramics this usually refers to a clay that has been dried but not fired or fired but not to a high enough temperature to glassify it (which makes it vitreous) so that it would be non-porous.
Pumice—a porous form of obsidian or volcanic glass that is frothy, spongy and light in appearance, usually dull gray in color, formed by trapped and escaping gases in a volcano.
Quartz—a naturally occurring crystal of silica either in pure form or with impurities, which cause it to have a wide range of colors and finishes. Quartz is the basic constituent of sandstone and quartzite. It also often contains gold.
Reduction—the atmosphere in a kiln which has insufficient air to support complete combustion. This will often cause smoke, which affects the surfaces of glazes and clays, and may also cause glaze or clay molecules which contains oxygen atoms to give up their oxygen to the atmosphere where it is consumed by combustible materials (the gas, wood, oil, or other things in a kiln, such as sawdust or other burnable items place in the kiln). See also oxidation and Raku.
Raw—glaze or clay which has not yet been fired. It may still be greenware or fully dried. See also bisque and final.
Raku—a method of low-fire surface change produced commonly by putting a red-hot piece into a bucket (called a "sagger"), which contains combustible material, typically sawdust, newspaper, leaves and even garbage. The temperature of the piece ignites the materials and they begin to smoke. A lid is then placed on the bucket, producing a reduction atmosphere, along with the effects of the smoke of the burning materials. Raku can also be accomplished in a "Raku kiln" where the piece is both fired and the Raku atmosphere created.
Red clay—this is actually the term that potters use to describe clay that is brown. When fired to 1000 C (1832 F), the clays will turn a deep orange color. Red clays will vitrify below 1200 C (2192 F).
Refractory—an adjective describing any material that melts at a very high temperature.
Resist decoration—sounds just like what it is. When a wax is painted onto a pot, that area will resist any coloring or glaze.
Sagger—1) a clay or bucket in which pieces are placed while inside a kiln, to protect them from the direct effect of flames, or 2) a clay (sometimes metal, like a garbage can) bucket, used to hold combustible materials (wood, paper, etc.).
Salt Glaze—by throwing salt into a kiln during the glaze firing, a shiny gloss will occur as it vaporizes and combines with the silica in the body of the ware.
Sgraffito—this is a design that can be made by scraping or scratching through a layer of slip that has been applied to reach the contrasting color of the clay body beneath.
Silica—a basic material of glaze and clay. In nature this is also known as quartz. In a glaze, promotes flow (fluxing). See also alumina.
Slip—this is clay that has been thinned, by the adding water to the clay.
Slurry—thick slip.
Soaking—by balancing the fuel intake in a kiln, vitrification temperature can be maintained. Instead of shutting off the kiln, or damping down when the desired temperature is reached, you would leave it for ten minutes or so, (soaking). This gives the glaze a more mature appearance.
Sprigging—this is a technique used by Wedgwood, where relief-molded decorations are applied to a leather hard pot.
Stoneware—non-porous, this pottery is fired to temperatures of about 1250 C. At the point of vitrification the glaze and body are partially fused together.
Tenmoku—stoneware glaze that is stained by iron oxide. Generally tenmokus are shiny glazes that are black or dark brown.
Temper—the addition of coarse non-plastic materials that can improve working and firing of the clay.
Tin Glaze—this is white and opaque glaze, made this way by the addition of tin oxide to the glaze.
Vitrification—the temperature that occurs during this process varies with each different clay. During firing, vitrification is simply the fusion of a clay body. This is necessary so that the clay body will reach the exact point of hardness at the same temperature that the glaze will melt to form the individual shiny coating over the ware. After vitrification, the clay can no longer be recycled, though it may be used as grog.
Wedging—putting the clay into a workable, smooth state, by kneading or by repeatedly cutting and slamming together lumps of moist clay.